Manhattan Project

Manhattan Project

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The Manhattan Project was the code name for the American-led effort to develop a functional atomic weapon during World War II. The controversial creation and eventual use of the atomic bomb engaged some of the world’s leading scientific minds, as well as the U.S. military—and most of the work was done in Los Alamos, New Mexico, not the borough of New York City for which it was originally named. The Manhattan Project was started in response to fears that German scientists had been working on a weapon using nuclear technology since the 1930s—and that Adolf Hitler was prepared to use it.

America Declares War

The agencies leading up to the Manhattan Project were first formed in 1939 by President Franklin D. Roosevelt, after U.S. intelligence operatives reported that scientists working for Adolf Hitler were already working on a nuclear weapon.

At first, Roosevelt set up the Advisory Committee on Uranium, a team of scientists and military officials tasked with researching uranium’s potential role as a weapon. Based on the committee’s findings, the U.S. government started funding research by Enrico Fermi and Leo Szilard at Columbia University, which was focused on radioactive isotope separation (also known as uranium enrichment) and nuclear chain reactions.

The Advisory Committee on Uranium’s name was changed in 1940 to the National Defense Research Committee, before finally being renamed the Office of Scientific Research and Development (OSRD) in 1941 and adding Fermi to its list of members.

That same year, following the Japanese attack on Pearl Harbor, President Roosevelt declared that the U.S. would enter World War II and align with Great Britain, France and Russia to fight against the Germans in Europe and the Japanese in the Pacific theater.

The Army Corps of Engineers joined the OSRD in 1942 with President Roosevelt’s approval, and the project officially morphed into a military initiative, with scientists serving in a supporting role.

The Manhattan Project Begins

The OSRD formed the Manhattan Engineer District in 1942, and based it in the New York City borough of the same name. U.S. Army Colonel Leslie R. Groves was appointed to lead the project.

Fermi and Szilard were still engaged in research on nuclear chain reactions, the process by which atoms separate and interact, now at the University of Chicago, and successfully enriching uranium to produce uranium-235.

Meanwhile, scientists like Glenn Seaborg were producing microscopic samples of pure plutonium, and Canadian government and military officials were working on nuclear research at several sites in Canada.

On December 28, 1942, President Roosevelt authorized the formation of the Manhattan Project to combine these various research efforts with the goal of weaponizing nuclear energy. Facilities were set up in remote locations in New Mexico, Tennessee and Washington, as well as sites in Canada, for this research and related atomic tests to be performed.

Robert Oppenheimer and Project Y

Theoretical physicist J. Robert Oppenheimer was already working on the concept of nuclear fission (along with Edward Teller and others) when he was named director of the Los Alamos Laboratory in northern New Mexico in 1943.

Los Alamos Laboratory—the creation of which was known as Project Y—was formally established on January 1, 1943. The complex is where the first Manhattan Project bombs were built and tested.

On July 16, 1945, in a remote desert location near Alamogordo, New Mexico, the first atomic bomb was successfully detonated—the Trinity Test—creating an enormous mushroom cloud some 40,000 feet high and ushering in the Atomic Age.

Scientists working under Oppenheimer had developed two distinct types of bombs: a uranium-based design called “the Little Boy” and a plutonium-based weapon called “the Fat Man.” With both designs in the works at Los Alamos, they became an important part of U.S. strategy aimed at bringing an end to World War II.

The Potsdam Conference

With the Germans sustaining heavy losses in Europe and nearing surrender, the consensus among U.S. military leaders in 1945 was that the Japanese would fight to the bitter end and force a full-scale invasion of the island nation, resulting in significant casualties on both sides.

On July 26, 1945, at the Potsdam Conference in the Allied-occupied city of Potsdam, Germany, the U.S. delivered an ultimatum to Japan—surrender under the terms outlined in the Potsdam Declaration (which, among other provisions, called for the Japanese to form a new, democratic and peaceful government) or face “prompt and utter destruction.”

As the Potsdam Declaration provided no role for the emperor in Japan’s future, the ruler of the island nation was unwilling to accept its terms.

Hiroshima and Nagasaki

Meanwhile, the military leaders of the Manhattan Project had identified Hiroshima, Japan, as an ideal target for an atomic bomb, given its size and the fact that there were no known American prisoners of war in the area. A forceful demonstration of the technology developed in New Mexico was deemed necessary to encourage the Japanese to surrender.

With no surrender agreement in place, on August 6, 1945, the Enola Gay bomber plane dropped the as-yet untested “Little Boy” bomb some 1,900 feet above Hiroshima, causing unprecedented destruction and death over an area of five square miles. Three days later, with still no surrender declared, on August 9th, the “Fat Man” bomb was dropped over Nagasaki, site of a torpedo-building plant, destroying more than three square miles of the city.

The two bombs combined killed more than 100,000 people and leveled the two Japanese cities to the ground.

The Japanese informed Washington, which following Roosevelt’s death was under the new leadership President Harry Truman, of their intention to surrender on August 10th, and formally surrendered on August 14, 1945.

Legacy of the Manhattan Project

With the development of weapons designed to bring about the end of World War II as its stated mission, it’s easy to think that the story of the Manhattan Project ends in August, 1945. However, that’s far from the case.

Following the end of the war, the United States formed the Atomic Energy Commission to oversee research efforts designed to apply the technologies developed under the Manhattan Project to other fields.

Ultimately, in 1964, then-President Lyndon B. Johnson put an end to the U.S. government’s effective monopoly over nuclear energy by allowing for private ownership over nuclear materials.

The nuclear fission technology perfected by the Manhattan Project engineers has since become the basis for the development of nuclear reactors, for power generators, as well as other innovations, including medical imaging systems (for example, MRI machines) and radiation therapies for various forms of cancer.


Manhattan: The Army and the Atomic Bomb. U.S. Army Center of Military History.
The Manhattan Project—Its Story. U.S. Department of Energy: Office of Scientific and Technical Information.
Leo Szilárd, a traffic light and a slice of nuclear history. Scientific American.
J. Robert Oppenheimer (1904—1967). Atomic Archive.

Manhattan Project Historical Resources

The U.S. Department of Energy (DOE) has developed and made available to the public a wide range of in-print, online, and in-person Manhattan Project historical resources. These include histories, websites, reports and document collections, and exhibits and tours.

DOE Histories of the Manhattan Project: Histories produced by the Department include The Manhattan Project, which provides a brief overview, and the longer, at 100 pages (including the 35-page "Photo Gallery") The Manhattan Project: Making of the Atomic Bomb. These non-technical, highly readable accounts are geared toward the general reader. Published in 1962, The New World, 1939-1946, was the first major Manhattan Project history. As Volume 1 of the official History of the Atomic Energy Commission series, The New World used both unclassified and still-classified source materials and revealed much that previously had not been disclosed. The New World and the U.S. Army Center of Military History's Manhattan: The Army and the Atomic Bomb released in 1985 remain the best-detailed published accounts of the Manhattan Project and are available at major libraries.

In July 2013, the Department launched The Manhattan Project: Resources, a web-based, joint collaboration between the Department’s Office of Classification and its History Program. The site is designed to disseminate information and documentation on the Manhattan Project to a broad audience including scholars, students, and the general public. The Manhattan Project: Resources consists of two parts: 1) The Manhattan Project: An Interactive History, a website history designed to provide an informative, easy-to-read, comprehensive overview of the Manhattan Project, and 2) the Manhattan District History, a multi-volume classified history commissioned by General Leslie Groves at the end of the war that assembled a vast amount of information in a systematic, readily available form and included extensive annotations, statistical tables, charts, engineering drawings, maps, and photographs. All 36 volumes of the Manhattan District History, declassified and declassified with redactions, are being made available full text online.

Manhattan Project Site Histories: Additional sources for information on the Manhattan Project can be found at the following sites hosted by the Department's field sites and laboratories: the Los Alamos National Laboratory's Our History, the Y-12 National Security Complex's Y-12 History, the Oak Ridge National Laboratory's history site, and Hanford's Hanford History. In conjunction with the opening of the Manhattan Project National Historical Park on November 10, 2015, the Department launched the K-25 Virtual Museum website.

Manhattan Project Images: DOE provides access to a variety of Manhattan Project images through its Flickr site.

Manhattan Project Records: The Department continues to release declassified Manhattan Project-related reports and documents on its OpenNet website. This searchable database includes bibliographical references to all documents declassified and made publicly available after October 1, 1994. Some documents can be viewed in full text. Unclassified and declassified Manhattan Project records collection can be accessed at the National Archives and Records Administration (NARA). The core administrative records of the Manhattan Engineer District (MED) came out of Oak Ridge, Tennesee, and have been transferred to NARA's Southeast Region located in Atlanta, Georgia. Also at Atlanta are unclassified/declassified MED operational division and other Oak Ridge records. Classified MED records were sent to NARA headquarters (Archives II in College Park).

Manhattan Project - HISTORY

The Manhattan Project not only set in motion events that would cement the outcome of the Second World War. The Manhattan Project also changed the entire way warfare would be fought forever. It also contributed to a complete change in the global positioning of superpowers, would be superpowers and their allies.

Of course, the original goal of the Manhattan Project (1942 to 1945) was to end World War Two. While this was the goal, not even those at the heart of the project truly realized how they would be forever changing and shaping history through their successful achievement of their goal: to develop and create functional atomic weapons.

The Splitting of the Atom

In the 1930s, it was discovered that the atom could be split in what is known as the fission process. In 1939, scores of American scientists would look for ways in which this process could be harnessed for military purposes. Ironically, many of the scientists that would work on this project were newly transplanted Europeans that had escaped fascist regimes in Europe. These scientists were now dedicating their lives to the defeat of these regimes.

The Early Stages of the Project

The first major step in what would eventually become the Manhattan Project was when, in 1939, the scientist Enrico Fermi would meet with representatives from the Department of the Navy. Soon after in the summer of 1939, the legendary thinker Albert Einstein would be asked to make a presentation to then President Franklin D. Roosevelt. In the presentation, Einstein showed that there was enormous military potential in the release of a totally uncontrollable fission chain reaction. Harnessed effectively, this chain reaction could be used to create a weapon like none had ever been seen on the earth before.

The very first stage of the project moved forward in early 1940. The original budget was a grant of $6,000 in research funding. Over the course of a nearly two years, the results were promising and the Office of Scientific Research and Development began to oversee the project on December 6, 1941.

The United States entered World War II in 1941 and the research surrounding the (yet unnamed project) would be moved to the Department of Defense. (Then called the War Department) The reason for the move was because the most superior talent in research, development, and the sciences was working in defense. Therefore, it was believed the greatest progress could be made if these same professionals took a direct, hands-on approach in the research of the weapons.

The Manhattan Project is Born

The Manhattan Project would eventually receive its official codename in 1942. This was thanks in large part of the delegation of much of the construction work being related to the project to the Corps of Engineers district office in Manhattan. One reason for this is that a great deal of the early research for the project was at Columbia University which was located in the Manhattan area.

One thing that must be understood about this project is that it was a massive one. While a lot of the work was performed in the Manhattan area, this section of New York City was not the only locale where research and development was being conducted. In truth, there were research offices located all throughout the United States handling various different tasks and treading into waters never before broached by scientific and military personnel.

An International Project

The United States was not the only country involved with such a project. Germany had launched its own in 1940 and to say this was of the gravest concern to the United States and Great Britain would be an understatement. Great Britain was also at work on its own project and would eventually work in a joint cooperative arrangement with the United States and Canada to help move the Manhattan Project along.

In 1943, some of the greatest scientific minds in the world would contribute their work to the Manhattan Project, helping to continue its progress.

Creating the Fission Chain

One of the major aspects of research was finding suitable source material for creating the fission chain. Uranium 238 was originally experimented on, but the results were futile. Uranium 235 became the next material to be subjected to fission chain processes, but it simply was not reliable enough and too much work was required in order to see clear results. Eventually, it was Plutonium 235 that would be the source compound that would be used to create the chain reaction.

The Concept of the Bomb

Prior to 1943, not very much work went into the development of the actual bomb that would be used to actually turn the fission chain into a weapon. Since limited progress had been made on actually splitting the atom, The path to actually creating the bomb would move at top speed when J. Robert Oppenheimer set up a laboratory in Los Alamos, New Mexico to work on creating and testing an actual bomb.

The scope of the Manhattan Project in New Mexico was to shrink down the amount of fissionable material that could still be enough to yield the critical mass of an explosion. This was in addition to being able to harness the chain reaction within a bomb that could reliably and effectively react when detonated.

The First Atomic Bomb Test

After $2 billion dollars of research and development, a workable prototype of an atomic bomb was made. During the early morning hours of July 16, 1945, the New Mexico desert became the site of the first atomic bomb test. The bomb exploded into the shape of a massive mushroom cloud. The force of the explosion was the equivalent to 20,000 tons of dynamite and the shock waves were felt for miles. Much of the surrounding test area for the bomb was vaporized. It was obvious the new super weapon worked and the time and money spent on the Manhattan Project delivered the desired results. The results were the creation of the most destructive weapon in human history up until that time.

Soon after, the atomic bomb would be used to end World War II via the bombings of Hiroshima and Nagasaki.

51f. The Manhattan Project

This once classified photograph features the first atomic bomb &mdash a weapon that atomic scientists had nicknamed "Gadget." The nuclear age began on July 16, 1945, when it was detonated in the New Mexico desert.

Early in 1939, the world's scientific community discovered that German physicists had learned the secrets of splitting a uranium atom. Fears soon spread over the possibility of Nazi scientists utilizing that energy to produce a bomb capable of unspeakable destruction.

Scientists Albert Einstein , who fled Nazi persecution, and Enrico Fermi , who escaped Fascist Italy, were now living in the United States. They agreed that the President must be informed of the dangers of atomic technology in the hands of the Axis powers. Fermi traveled to Washington in March to express his concerns to government officials. But few shared his uneasiness.

Leaving nothing to chance, Los Alamos atomic scientists conducted a pre-test test in May 1945 to check the monitoring instruments. A 100-ton bomb was exploded some 800 yards from the Trinity site where Gadget would be detonated a few weeks later.

Einstein penned a letter to President Roosevelt urging the development of an atomic research program later that year. Roosevelt saw neither the necessity nor the utility for such a project, but agreed to proceed slowly. In late 1941, the American effort to design and build an atomic bomb received its code name &mdash the Manhattan Project .

At first the research was based at only a few universities &mdash Columbia University, the University of Chicago and the University of California at Berkeley. A breakthrough occurred in December 1942 when Fermi led a group of physicists to produce the first controlled nuclear chain reaction under the grandstands of Stagg Field at the University of Chicago.

Enrico Fermi, a physicist who left fascist Italy for America, encouraged the U.S. to begin atomic research. The result was the top-secret "Manhattan Project."

After this milestone, funds were allocated more freely, and the project advanced at breakneck speed. Nuclear facilities were built at Oak Ridge, Tennessee and Hanford, Washington. The main assembly plant was built at Los Alamos, New Mexico . Robert Oppenheimer was put in charge of putting the pieces together at Los Alamos. After the final bill was tallied, nearly $2 billion had been spent on research and development of the atomic bomb. The Manhattan Project employed over 120,000 Americans.

Secrecy was paramount. Neither the Germans nor the Japanese could learn of the project. Roosevelt and Churchill also agreed that Stalin would be kept in the dark. Consequently, there was no public awareness or debate. Keeping 120,000 people quiet would be impossible therefore only a small privileged cadre of inner scientists and officials knew about the atomic bomb's development. In fact, Vice-President Truman had never heard of the Manhattan Project until he became President Truman.

Although the Axis powers remained unaware of the efforts at Los Alamos, American leaders later learned that a Soviet spy named Klaus Fuchs had penetrated the inner circle of scientists.

This crater in the Nevada desert was created by a 104 kiloton nuclear bomb buried 635 feet beneath the surface. It is the result of a 1962 test investigating whether nuclear weapons could be used to excavate canals and harbors.

By the summer of 1945, Oppenheimer was ready to test the first bomb. On July 16, 1945, at Trinity Site near Alamogordo, New Mexico , scientists of the Manhattan Project readied themselves to watch the detonation of the world's first atomic bomb. The device was affixed to a 100-foot tower and discharged just before dawn. No one was properly prepared for the result.

A blinding flash visible for 200 miles lit up the morning sky. A mushroom cloud reached 40,000 feet, blowing out windows of civilian homes up to 100 miles away. When the cloud returned to earth it created a half-mile wide crater metamorphosing sand into glass. A bogus cover-up story was quickly released, explaining that a huge ammunition dump had just exploded in the desert. Soon word reached President Truman in Potsdam, Germany that the project was successful.

Effects of the Manhattan Project Going Forward

The bombings of Hiroshima and Nagasaki were not the end of research into and the subsequent development of even more potent atomic weapons. Today, modern nuclear bombs have 80 times the strength of the bomb dropped on Hiroshima. The mushroom cloud produced over Hiroshima, when compared to the estimated mushroom cloud of modern atomic bombs, is smaller than 1% of its modern counterpart. That is a terrifying thought as literally just the detonation of one of these modern atomic bombs would spell the end of nearly all life on Earth.

Even after having witnessed first-hand the sheer destruction these bombs brought with them, countries after the end of World War 2 only sought to create atomic bombs of their own. A nuclear arms race commenced between the big players, and there was a time of such uncertainty between the Soviet Union and the United States that many citizens of both nations went to bed every night wondering if they would get to wake up and see the sunrise one more time.

The History of a Park Dedicated to the Manhattan Project Story

This 2016 photo shows a view of the Hanford Site's B Reactor National Historic Landmark, a vibrant tourism and education draw that is part of the Manhattan Project National Historical Park.

The Manhattan Project was an unprecedented, top-secret research and development program created during World War II to develop an atomic weapon.

The beginning of the atomic age is recognized as one of the most important events of the 20th century. Its profound legacies include the proliferation of nuclear weapons, vast environmental remediation efforts, the development of the national laboratory system, and peaceful uses of nuclear materials such as nuclear medicine.

In 2001, DOE worked with the Advisory Council on Historic Preservation and a panel of distinguished historic preservation experts to develop preservation options for six DOE-owned Manhattan Project-era historic facilities that the panel found to be of extraordinary historical significance and worthy of “commemoration as national treasures.”

In 2004, Congress directed the National Park Service (NPS) to work with DOE to evaluate whether it was appropriate and feasible to establish a new unit of the national park system dedicated to telling the story of the Manhattan Project.

After a decade of work by local communities, elected officials, DOE, NPS, and other stakeholders, the Manhattan Project National Historical Park was authorized as part of the Carl Levin and Howard P. “Buck” McKeon National Defense Authorization Act for Fiscal Year 2015. The park includes facilities at the three primary Manhattan Project locations — Los Alamos, Oak Ridge, and Hanford.

At Los Alamos, more than 6,000 scientists and support personnel worked to design and build the atomic weapons. The park currently includes three areas there: Gun Site, which was associated with the design of the “Little Boy” bomb V-Site, which was used to assemble components of the Trinity device and Pajarito Site, which was used for plutonium chemistry research.

The Clinton Engineer Works, which became the Oak Ridge Reservation, supported three parallel industrial processes for uranium enrichment and experimental plutonium production.

The park includes the X-10 Graphite Reactor National Historic Landmark, which produced small quantities of plutonium to support Los Alamos weapons work buildings at the Y-12 complex, home to the electromagnetic separation process for uranium enrichment and the site of the K-25 building, where gaseous diffusion uranium enrichment technology was pioneered.

The Hanford Engineer Works, now the Hanford Site, was home to more than 51,000 workers who constructed and operated a massive industrial complex to fabricate, test, and irradiate uranium fuel in reactors and then chemically separate out plutonium to be used in weapons.

The Hanford landscape is also representative of one of the first acts of the Manhattan Project — the condemnation of private property and eviction of homeowners and American Indian tribes to clear the way for the top-secret work. The park includes the B Reactor National Historic Landmark, which produced the material for the Trinity Test and plutonium bomb and four turn-of-the-century historic buildings that give visitors a glimpse into the history of the Hanford area before the arrival of the Manhattan Project.

The park is managed as a collaborative partnership between DOE, which continues to own, preserve, and maintain the park facilities and will work to expand public access to them and NPS, which administers the park, interprets the story of the Manhattan Project, and provides technical assistance to DOE on historic preservation. A memorandum of agreement between DOE and the U.S. Department of the Interior signed in November 2015 officially created the park and guides implementation of the park mission by the two agencies.

While a key component of the national historical park mission within DOE is enhancing public access to the park facilities, DOE and its contractors are also working to develop online resources so virtual visitors and students can learn about the historic facilities and the Manhattan Project.

This DOE webpage offers a wide range of in-print, online, and in-person Manhattan Project historical resources. The Department also produced podcasts on the history and impact of the Manhattan Project.

At the Los Alamos park unit, the Bradbury Science Museum, operated by Los Alamos National Laboratory, provides numerous electronic resources, including an overview of the park and Project Y in Los Alamos, and an overview of Manhattan Project sites on laboratory land. The Bradbury Science Museum’s online collections database allows visitors to search artifacts, photos, and historic documents from the Manhattan Project. LANL has also produced a video of historic sites and work to preserve them for future generations.

Oak Ridge's K-25 Virtual Museum offers visitors information about the Manhattan Project and Cold war.

The Hanford park unit is accessible to virtual visitors through a variety of resources, including those provided by partners in the community. DOE offers virtual access to the B Reactor National Historic Landmark via a 360-degree camera system.

The Hanford History Project (HHP) at Washington State University Tri Cities preserves DOE’s federal Manhattan Project and Cold War collection of artifacts and oral histories. Virtual access to these collections, as well as the HHP’s collections of oral histories, donated archive materials, documents, and photographs are available at HHP’s website.

The B Reactor Museum Association provides a series of videos with in-depth information on how the B Reactor functions and why it is recognized as a scientific and engineering marvel.

Female Scientists of the Manhattan Project

Dr. Marie Curie

  • Marie Sklodowska was born in Warsaw Poland in 1867, to a mathematics and physics teacher.
  • Unable to attend a university because she was a woman, Marie attended “Flying University” a underground college.
  • Marie moved to Paris in 1891, in order to pursue a degree in physics and mathematics.
  • After receiving her master’s degree Marie began working with Pierre Curie, who later became her husband.
  • Marie and Pierre Curie discovered two new elements, polonium and radium, and coined the term radioactivity.
  • In 1903, Marie Curie became the first woman to earn her doctoral degree in France.
  • Marie and Pierre were awarded the Nobel Prize for their work in Physics in 1903.
  • In 1911, Marie Curie was awarded the Nobel Prize in Chemistry.
  • During WWI Curie devoted her time to helping wounded soldiers and bought war bonds with her Nobel Prize money.

Dr. Lise Meitner

  • Lise Meitner was born in Austria to a Jewish family in 1878.
  • Meitner became the second woman to earn a doctoral degree in physics at the University of Vienna in 1905.
  • After graduation Meitner moved to Berlin and began working with Otto Hahn where they discovered several new isotopes.
  • In 1922, Meitner became the first woman in Germany to become a full professor in physics at the University of Berlin.
  • In 1938, Meitner was forced to travel in secret out of Berlin to Sweden where she would continue her work.
  • Six months later Meitner and Otto Frisch published results explaining and naming nuclear fission.
  • Although nominated several times, Lise did not receive the Nobel Prize for her work. Otto Hahn was given the award.
  • Offered a position on the Manhattan Project, Meitner refused the work stating “I will have nothing to do with a bomb.”
  • Element 109, discovered in 1997, was named in her honor. Meitnerium.

Dr. Leona Woods Marshall Libby

Dr. Leona Woods Marshall Libby

  • Leona graduated high school at age 14 and from the University of Chicago with a BS in chemistry at the age of 19.
  • While completing her Ph.D. Woods was assigned to work on the Chicago Pile where she constructed the neutron detectors used to gage the flow of flow on neutrons in the pile.
  • Leona was also the only female scientist at the Hanford site and worked directly with Enrico Fermi.
  • Dr. Libby went on to have a successful career teaching at several universities before taking a position at UCLA as a visiting professor, in 1973.
  • Dr. Libby’s research included the study of rainfall patterns in tree rings hundreds of years before records were kept. This opened the door for climate change research.

The work of the Manhattan Project

In the initial stages of the American fission effort (1939-1942), scientists at a variety of university laboratories — notably Columbia University, the University of Chicago, and the University of California–Berkeley, among many others— identified key processes for the development of the “fissile material” fuel that is necessary for a nuclear weapon to operate.

The first approach considered was the isotopic enrichment of uranium. (Chemical elements can vary in the number of neutrons in their nucleus, and these different forms are known as isotopes.) It was discovered as early as 1939 that only one isotope of uranium was fissionable by neutrons of all energies, and by 1941 it was understood that to make a fission weapon required a reasonably pure amount of material that met this criterion. Less than 1% of the uranium as mined is the fissile uranium-235 isotope, with the other 99% being uranium-238, which inhibits nuclear chain reactions. It was understood by 1941 that to make a weapon the fissile uranium-235 would need to be separated from the non-fissile uranium-238, and that because they were chemically identical this could only be accomplished through physical means that relied on the small (three neutron) mass difference between the atoms. Isotopic separation had been undertaken for other elements (for example, the separation of the hydrogen isotope deuterium from the bulk of natural water), but never on a scale of the sort contemplated for the separation of uranium. 16

Several methods were proposed and explored at small scales at various research sites in the United States. The preferred candidates by the end of the first year of the Manhattan Project (1942) were:

Electromagnetic separation, in which powerful magnetic fields were used to create looping streams of uranium ions that would slightly concentrate the lighter isotope at the fringes. This work was related to the cyclotron concept pioneered by Ernest Lawrence at the University of California, and the bulk of the research took place at his Radiation Laboratory.

Gaseous diffusion, in which a gaseous form of uranium was forced through a porous barrier consisting of extremely fine passageways. The gas molecules containing the lighter isotope would navigate the barrier slightly faster than the gas molecules containing the heavier isotope, although the effect would have to be magnified through many stages before it resulted in significant separation. This work was originally explored primarily at Columbia University under the guidance of Harold Urey and others.

Thermal diffusion, in which extreme heat and cold were applied to opposite sides of a long column of uranium gas, which also resulted in slight separation, with the lighter uranium isotope concentrating at one end. This was initially investigated by Philip Abelson at the Naval Research Laboratory.

Centrifugal enrichment, in which the rapid spinning of a uranium gas allowed for the slight concentration of the lighter element at the center of the whirling mixture, a process that would also require a large number of “stages” to be successful. This was pursued by physicist Jesse W. Beams at the University of Virginia and at the Standard Oil Development Company in New Jersey. 17

Over the course of 1943, centrifugal enrichment proved less promising than the other methods, and by 1944 the method was essentially abandoned (though it would, in the postwar period, be perfected by German and Austrian scientists working in the Soviet Union). Because it was unclear which of the other techniques would be most successful at scale, both the electromagnetic and gaseous diffusion methods were pursued with great gusto, and arguably constituted the most substantial portion of the Manhattan Project. The construction and operation of the two massive facilities required for these methods (the Y-12 facility for the electromagnetic method, and K-25 facility for the gaseous diffusion method) alone made up 52% of the cost of the overall project, and all of the Oak Ridge facilities together totaled 63% of the entire project cost. While thermal diffusion was initially imagined as a competitor process, difficulties in achieving the desired level of enrichment led to all three methods being “chained” together as a sequence: the raw uranium would be enriched from the natural level of 0.72% uranium-235 to 0.86% at the thermal diffusion plant, and its output would then be enriched to 23% at the gaseous diffusion plant, and then finally enriched to an average level of 84% at the electromagnetic plants. 18

Image 3: Calutron operators at the Y-12 plant in Oak Ridge monitored indicators and turned dials in response to changing values, not knowing that they were actually aiming streams of uranium ions, much less that they were producing the fuel for a new weapon. Source: Photo by Ed Westcott, 1944 (Department of Energy).

The plants for the production of enriched uranium were constructed in Oak Ridge, Tennessee, an isolated site that was chosen primarily for its proximity to the large electrical resources provided by the Tennessee Valley Authority. The Oak Ridge site (Site X) employed over 45,000 people for construction at its peak, and had a similar number of employees on the payroll for managing its continued operations once built. A “secret city,” the facility relied on heavy compartmentalization (“need to know”) so that practically none of its thousands of employees had any real knowledge of what they were producing. Every aspect of life in Oak Ridge was controlled by contractors and the military, in the aim of producing weapons-grade material in maximum haste and with a minimum of security breaches. Situated in the Jim Crow South, the facility was entirely segregated by law, and living conditions between African-Americans and whites varied dramatically. Various industrial contractors managed the different plants (for example, the Union Carbide and Carbon Corporation operated K-25, and the Tennessee Eastman Corporation operated Y-12). 19

In the process of researching the possibility of nuclear fission, another road to a bomb had made itself clear. Nuclear reactors had been contemplated as early as nuclear weapons. Where a nuclear weapon requires high concentrations of fissile material to function, a reactor does not: a controlled nuclear reaction (as opposed to an explosive one) can be developed through natural or slightly-enriched uranium through the use of a substance called a “moderator,” which slows the neutrons released from fission reactions. Under the right conditions, this allows a chain reaction to proceed even in unenriched material, and the reaction is considerably slower, and much more controllable, than the kind of reaction that occurs inside of a bomb.

Nuclear reactors had been explored as possible energy sources, though engineering difficulties would make this use of them more difficult than was anticipated (the first nuclear reactors for power purposes in the United States did not go critical until 1958). More importantly for the wartime planners, it was realized that the plentiful uranium-238 isotope, while not fissile, could still be quite useful. When uranium-238 absorbs a neutron, it does not undergo fission, but instead transmutes into uranium-239. Uranium-239, however, is unstable, and through a series of nuclear decays becomes, in the span of a few days, the artificial element plutonium-239. Isolated for the first time in February 1941, plutonium was calculated and confirmed to have very favorable nuclear properties (it is even more reactive than uranium-235, and thus even less of it is necessary for a chain reaction). 20

Image 4: Men working on the front face of the Hanford B-Reactor, circa 1944. Source: Department of Energy.

The first controlled nuclear reaction was achieved in December 1942 at the University of Chicago, by a team led by Enrico Fermi. The first reactor, Chicago Pile-1, used purified graphite as its moderator and 47 tons of natural (unenriched) uranium in the form of metal ingots. Even while the pilot Chicago Pile-1 reactor was still being constructed, plans were being made for the creation of considerably larger, industrial-sized nuclear reactors at a remote site in Hanford, Washington, constructed and operated by E.I. du Pont Nemours & Co. (DuPont). The Hanford site (Site W) was chosen largely for its proximity to the Columbia River, whose water would be used for cooling purposes. On dusty land near the river, three large graphite-moderated reactors were constructed starting in 1943, with the first reactor going critical in September 1944. A massive chemical facility known as a “canyon” was constructed nearby, by which, largely through automation and remote control, the irradiated fuel of the reactors was chemically stripped of its plutonium. This process involved dangerously radioactive materials, chemically noxious substances (powerful acids), and was fairly inefficient (every ton of uranium fuel that was processed yielded 225 grams of plutonium). 21

The labor conditions at Hanford varied considerably from Oak Ridge. Where Oak Ridge was imagined as a cohesive community, Hanford was not, and employed an abundance of cheap labor in far inferior work conditions (and those at Oak Ridge were not so great to begin with). The radioactive and chemical wastes at the site were treated in an expedient, temporary fashion, with the idea that in the less-hurried future they would be more properly eliminated. Subsequent administrations continued this approach for decades. Hanford became regarded as the most radioactively contaminated site in the United States, and since the end of the Cold War has been involved in expensive cleanup and remediation efforts. The Hanford project constituted about 21% of the total cost of the Manhattan Project. 22

Image 5: The relative costs (in 1945 USD) of the major expense categories of the Manhattan Project. Note that Oak Ridge has been broken down into its subcomponents (K-25, Y-12, S-50, etc.). Source: Data from Hewlett and Anderson 1962, Appendix 2, graph by Alex Wellerstein.

The work of these two sites — Oak Ridge and Hanford — constituted the vast bulk of the labor and expense of the Manhattan Project (roughly 80% of both). Without fuel, there could be no atomic bomb: it was and remains a key chokepoint in the development of nuclear weapons. As a result, it is important to conceptualize the Manhattan Project as much more than just basic science alone: without an all-out military-industrial effort, the United States would not have had an atomic bomb by the end of World War II.

The head of the Manhattan Project’s entire operation was Brigadier General Leslie R. Groves, a West-Point trained engineer who had previously been instrumental in the construction of the Pentagon building. Groves had accepted the assignment reluctantly, liking neither the risk of failure nor the fact that it was a home-front assignment. But once he accepted the job, he was determined to see it through to success. His unrelenting drive resulted in the Manhattan Project being given the top level of priority of all wartime projects in the United States, which allowed him nearly unfettered access to the resources and labor necessary to build a new atomic empire. Groves amplified the degree of secrecy surrounding the project through his application of compartmentalization (which he considered “the very heart of security”), and his own autonomous domestic and even foreign intelligence and counter-intelligence operations, making the Manhattan Project a virtual government agency of its own. (Despite these precautions, the project was, it later was discovered, compromised to the Soviet Union by several well-placed spies.) While it is uncharacteristic to associate the success or failure of massive projects with single individuals, it has been plausibly argued that Groves was perhaps the most “indispensable” individual to the project’s success, and that his willingness to accelerate and amplify the work being done in the face of setbacks, and to bully his way through military and civilian resistance, was essential to the project achieving its results when it did. 23

Though the scientific research on the project was initially dispersed among several American universities, as the work moved further into the production phase civilian and military advisors to the project concurred that the most sensitive research work, specifically that on the design of the bomb itself, should be located somewhere more secure than a university campus in a major city. Bush, Conant, and Arthur Compton had all come to the conclusion that a separate, isolated laboratory should be created for this final phase of the work. In late 1942, Groves identified Berkeley theoretical physicist J. Robert Oppenheimer as his preferred candidate for leading the as-yet-created laboratory, and on Oppenheimer’s recommendation identified a remote boys’ school in Los Alamos, New Mexico, as the location for the work. Initially imagined to be fairly small, the Los Alamos laboratory (Site Y) soon became a sprawling operation that took on a wide variety of research projects in the service of developing the atomic bomb, ending the war with over 2,500 people working at the site. 24

Image 6: The percentage distribution of personnel between divisions at Los Alamos. The reorganization in August 1944 merged several divisions into interdisciplinary groups focused around specific problems. The pre-reorganization division abbreviations: Chem = Chemistry, Eng = Engineering, Ex = Experimental Physics, Theo = Theoretical Physics,. The post-reorganization abbreviations: A = Administrative, CM = Chemistry & Metallurgy, F = Fermi (whose division studied many issues), G = Gadget, O = Ordnance, R = Research, Tr & A = Trinity and Alberta (Testing and Delivery), X = Explosives. Source: Hawkins 1983, 302.

Though the work of the bomb was even at the time most associated with physicists, it is worth noting that at Los Alamos, there were roughly equal numbers of physicists, chemists, metallurgists, and engineers. The physics-centric narrative, promulgated in part by the physicists themselves after the war (in part because the physics of the atomic bomb was easier to declassify than other aspects), obscures the multidisciplinary research work that was required to turn table-top laboratory science into a working weapon. 25

It is not exceptionally hyperbolic to say that the Los Alamos laboratory brought together the greatest concentration of scientific luminaries working on a single project that the world had ever seen. It was also highly international in its composition, with a significant number of the top-tier scientists having been refugees from war-torn Europe. This included a significant British delegation of scientists, part of an Anglo-American alliance negotiated by Winston Churchill and Roosevelt. For the scientists who went to the laboratory, especially the junior scientists who were able to work and mingle with their heroes, the endeavor took on the air of a focused and intensive scientific summer camp, and the numerous memoirs about the period at times underemphasize that the goal was to produce weapons of mass destruction for military purposes. 26

Los Alamos grew because the difficulty and scope of the work grew. Notably a key setback motivated a massive reorganization of the laboratory in the summer of 1944, when it was found that plutonium produced by nuclear reactors (as opposed to the small samples of plutonium that had been produced in particle accelerators) could not be easily used in a weapon. The original plan for an atomic bomb design was relatively simple: two pieces of fissile material would be brought together rapidly as a “critical mass” (the amount of material necessary to sustain an uncontrolled chain reaction) by simply shooting one piece into the other through a gun barrel using conventional explosives. This “gun-type” design still involved significant engineering considerations, but compared to the rest of the difficulties of the project it was considered relatively straightforward. 27

The first reactor-bred samples of plutonium, however, led to the realization that the new element could not be used in such a configuration. The presence of a contaminating isotope (plutonium-240) increased the background neutron rate of reactor-bred plutonium to levels that would pre-detonate the weapon were two pieces of material to be shot together, leading to a significantly reduced explosion (designated a “fizzle”). Only a much faster method of achieving a critical mass could be used. A promising, though ambitious, method had been previously proposed, known as “implosion.” This required the creation of specialized “lenses” of high explosives, arranged as a sphere around a subcritical ball of plutonium, that upon simultaneous detonation would symmetrically squeeze the fuel to over twice its original density. If executed correctly, this increase in density would mean that the plutonium in question would have achieved a critical mass and also explode. But the degree of simultaneity necessary to compress a bare sphere of metal symmetrically is incredibly high, a form of explosives engineering that had scarcely any precedent. Oppenheimer reorganized Los Alamos around the implosion problem, in a desperate attempt to render the plutonium method a worthwhile investment. Modeling the compressive forces, much less achieving them (and the levels of electrical simultaneity necessary) required yet another massive multidisciplinary effort. 28

As of summer 1944, there were two designs considered feasible: the “gun-type” bomb which relied upon enriched uranium from Oak Ridge, and the “implosion” bomb which relied upon separated plutonium from Hanford. The manufacture of the factories that produced this fuel required raw materials, equipment, and logistics from many dozens of sites, and together with the facilities that were involved with producing the other components of the bomb, there were several hundred discrete locations involved in the Manhattan Project itself, differing dramatically in size, location, and character. To choose a few interesting examples: a former playhouse in Dayton, Ohio, was converted into the site for the production of the highly-radioactive and highly-toxic substance polonium, which was to be used as a neutron source in the bombs, without any knowledge of the residents who lived around it most of the uranium for the project was procured from the Congo and a major reactor research site was created in Quebec, Canada, as part of the British contribution to the work. 29

Image 7: The assembled implosion “gadget” of the Trinity test, July 1945, with physicist Norris Bradbury for scale. Source: Los Alamos National Laboratory.

The uncertainties involved in the implosion design meant that the scientists were not confident that it would work and, if it did work, how efficient, and thus explosive, it would be. A full-scale test of the implosion design was decided upon, at a remote site at the White Sands Proving Ground, 60 miles from Alamogordo, New Mexico. On July 16, 1945, the test, dubbed “Trinity” by Oppenheimer, was even more successful than expected, exploding with the violence of 20,000 tons of TNT equivalent (20 kilotons, in the new standard of explosive power developed by the project participants). 30 (They had considerably more confidence in the gun-type bomb, and in any case, lacked enough enriched uranium to contemplate a test of it.)

Along with the work of the creation of the key materials for the bombs and the weapons designs themselves, additional thought was put into the question of “delivery,” the effort that would be required to detonate the bomb over a target. This aspect of the project, more a concern of engineering than science per se, was itself nontrivial: the atomic bombs were exceptionally heavy by the standards of the time, and the implosion bomb in particular had an ungainly egg-like shape. The “Silverplate” program created modified versions of the B-29 Superfortress long-range heavy bombers (most of their armaments and all of their armor were removed so that they could fly higher and faster with the heavy bombs), while Project Alberta, headquartered at Wendover Army Air Field in Utah, developed the ballistic cases of the weapons while training crews in the practice of delivering such weapons with relative accuracy. 31

Beginning in 1943, Project Y – the code name for Los Alamos during World War II – transformed the isolated Pajarito Plateau. The sounds of construction equipment replaced the voices of the Los Alamos Ranch School boys and local homesteaders. Construction crews hurriedly built many structures on mesa tops and in the canyons of Los Alamos. Countless concerns flooded Manhattan Project staff, but desiging structures to withstand the test of time was not one of them. The top-secret race to develop an atomic bomb before Nazi Germany was on and everyone felt the pressure.

Over the next 75 years, some of the structures slumped into disrepair from exposure to the harsh northern New Mexico environment — concrete cracking and spalling, wood frames rotting. That’s where Los Alamos National Laboratory’s historic preservation team enters the Manhattan Project story.

“Concrete has proven to be especially susceptible to the dozens of freeze-thaw cycles that often take place on a winter day in Los Alamos,” said Jeremy Brunette from the Laboratory’s Historic Building Surveillance and Maintenance Program.

The Manhattan Project National Historical Park team at Los Alamos identified several sites that need attention, and they work continuously to maintain, restore, and protect these historic sites. Most recently, two sites that share different stories from the early years of the Laboratory underwent preservation work.

Overshadowed story: plutonium recovery

A story that is often overshadowed when sharing Manhattan Project history is that of plutonium recovery. The Concrete Bowl helps bring that story to life.

Throughout the Manhattan Project, uranium and plutonium were so rare and costly that scientists carefully conserved every gram. By the end of 1945, it cost an estimated $390 million to create the plutonium for the Manhattan Project — that is over $5 billion in today’s money! During the Trinity Test, scientists planned to carry out a test with half the world’s plutonium, so tensions were understandably high.

If the Trinity Test did not succeed, project staff needed to recover the precious plutonium rather than losing it on a failed test. Manhattan Project researchers discussed several possible plutonium recovery approaches and tested any potential solutions that were not too far-fetched. One idea was the “water recovery method.”

For this method, staff members constructed a concrete bowl 200 feet in diameter and built a wooden water tank on a tower in the center. In this water tank, they placed a small-scale, industrial prototype of a bomb that contained natural uranium as a stand-in for plutonium. Researchers then detonated this mock-up with conventional explosives inside the water tank.

The water from the explosion landed in this concrete reservoir and drained into the bowl’s filter system, where workers recovered the metal fragments. Scientists continued these water-recovery tests until early 1945, but after realizing this method was not feasible for a full-scale nuclear test, they moved on to other potential recovery methods—including the infamous giant steel containment vessel known as “Jumbo.”

The Concrete Bowl remains in place today—an example of the wartime Laboratory’s practice of simultaneously testing different solutions to solve complex problems. In the 75 years since the bowl’s construction, weeds and trees took over and the local fauna discovered it as a reliable watering hole on the arid Pajarito Plateau.

“One of the pleasures of working at the Concrete Bowl is the amount of wildlife in the area. We saw elk, deer and coyotes every day,” Brunette said.

Concrete bowl before restoration. Concrete bowl after restoration.

Brunette also described that “in the Concrete Bowl, the steel reinforcing mesh was placed too close to the surface, exposing it to the elements and allowing it to carry moisture and rust into the concrete.”

Before any work began, the Lab’s Environmental Protection and Compliance Division ensured there was no contamination remaining from these early tests at the site. The Lab’s Historic Buildings team worked with Vital Consulting Group from Albuquerque on the removal of damaging vegetation to preserve this unique historic site. Vital Consulting Group also graded the soil away from the bowl to reduce the accumulation of water inside the bowl.

While the deer and elk may need to find a new watering hole, these efforts will preserve this historic site for years to come.

An early wartime test facility

From the beginning of Project Y, Robert Oppenheimer and Manhattan Project physicists believed they could make a “gun-type” atomic bomb, but they had to perfect the mechanism that could cause a sustained chain reaction in fissionable material. Manhattan Project researchers developed the Gun Site, known in 1943 as Anchor Ranch Proving Ground, to design and test nuclear weapon prototypes.

At this site, scientists, engineers, ordinance experts, and members of the U.S. Navy conducted experiments on the inner workings of this design. The name Gun Site refers to this site’s role in the development of the uranium weapon, Little Boy.

Because researchers fired numerous “gun-assembly” tests at this site using special gun barrels made by the U.S. Navy, they needed bunkers for protection during their experiments. Manhattan Project engineers constructed the buildings in a natural drainage, placing the tests above the bunkers and lessening the hazards of these experiments.

Scientists observed the tests from inside the concrete and earthen bunkers using a wooden periscope tower that relied on an elaborate system of mirrors—like a milk carton periscope you may have made as a child.

Gun Site during Manhattan Project—the wooden periscope tower is visible in the back right of the image.

Today, the preservation mission for this site came back to a familiar issue—concrete. Brunette explains why Manhattan Project era concrete presents the greatest preservation challenge. “We find that much of the Manhattan Project era concrete was mixed using large, smooth river rock aggregate that would not be suitable for modern construction.”

The buildings at Gun Site underwent extensive concrete repairs in 2012, including the reconstruction of the concrete parapet wall and a concrete cap to drain water from the top. However, that concrete cap failed and allowed further degradation of the historic site. The Lab and Vital Consulting Group worked to remove the crumbling concrete from the 2012 project. With this work completed, the Manhattan Project team will move forward with additional preservation efforts at Gun Site.

Gun Site parapet wall and cap before restoration. Gun Site parapet wall and cap after restoration.

These unique sites tell the story of Los Alamos National Laboratory’s history of solving difficult scientific and technological challenges and the story of a collective effort to achieve a common goal. The Manhattan Project was an immense project that created new fields of science and shaped the world we live in today.

In the spirit of its namesake, collaboration and teamwork defines the Manhattan Project National Historical Park. The National Park Service, the Department of Energy National Nuclear Security Administration’s Los Alamos Field Office, and Los Alamos National Laboratory work together to protect these sites for future generations. Ensuring that important historic sites remain intact to tell the story of this world-changing event is a crucial component of the collaborative effort to administer the Manhattan Project National Historical Park. The team is not finished they have already begun preservation work in another significant Manhattan Project historic location, V-Site.

The Manhattan Project National Historical Park

Preserving and sharing the nationally significant historic sites, stories, and legacies associated with the top-secret race to develop an atomic weapon during World War II.

This photo, taken on December 4, 1946, shows the center of Los Alamos as it looked during Project Y years. Called Technical Area 1, it was the core of the original laboratory.

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In 1943, as World War II raged across the globe, the United States government secretly constructed a laboratory on a group of isolated mesas in northern New Mexico. The top-secret Manhattan Project had a single military purposedevelop the world’s first atomic weapons.  

The success of this unprecedented government program forever changed the world. Join us to discover the stories of the people behind the Manhattan Project and how they shaped the world we live in today.

Scientists, engineers, explosive experts, military personnel, and members of the Special Engineer Detachment all convened on the rural Pajarito Plateau in New Mexico for a secret project during World War II. Their mission: develop an atomic weapon before Nazi Germany. General Leslie R. Groves selected J. Robert Oppenheimer, a theoretical physicist from the University of California at Berkeley, as the scientific project director. This unprecedented undertaking required revolutionary science, engineering, technological innovation, and collaboration between civilians and military personnel from diverse backgrounds.

Twenty-eight months after Project Y began in Los Alamos, members of the Manhattan Project detonated the world’s first atomic weapon, the "Gadget," at the Trinity Site in southern New Mexico. After the military deployment of two atomic weapons on the Japanese cities of Hiroshima and Nagasaki, and the subsequent end of World War II, some Los Alamos scientists took their families and returned to their pre-war lives. Yet, many stayed to continue critical research in this new Nuclear Age.

Today, Los Alamos National Laboratory remains one of the United States’ premier science and technology institutions. Cutting-edge research and technological breakthroughs still happen here, as scientists and engineers work to solve some of today’s most complex problems.

The Manhattan Project’s legacy of revolutionary science and engineering, along with the lessons learned from that time, continues in the spirit of the modern Laboratory. Scientific and technological advances made in the pursuit of an atomic weapon contributed to progress in many areas: environmental and materials science, biology, nuclear medicine, nuclear energy, supercomputing, precision machining, even astronomy. This was also the beginning of the Department of Energy’s National Laboratory System.

The U.S. Congress directs the National Park Service and the Department of Energy to determine the significance, suitability, and feasibility of including signature facilities remaining from the Manhattan Project in a national historical park. This was an effort to preserve remaining structures in order to save them from being lost forever.  

The National Defense Authorization Act, signed by President Obama, authorizes the creation of Manhattan Project National Historical Park. The stated the purpose of the park is “to improve the understanding of the Manhattan Project and the legacy of the Manhattan Project through interpretation of the historic resources.” On November 10, 2015, a Memorandum of Agreement signed by the Secretary of the Interior and the Secretary of the Department of Energy makes the park a reality.

Three sites tell the story of more than 600,000 Americans working to help end World War II. These three locations, integral to the Manhattan Project, comprise the park today.

    designed and built the first atomic bombs.   enriched uranium needed for the gun-type fission weapon.   created plutonium for an implosion-type weapon design.


The Manhattan Project National Historical Park encompasses 17 sites on Los Alamos National Laboratory property and 13 sites in downtown Los Alamos, where “Project Y” was centered during World War II. These sites represent the world-changing history of the Manhattan Project at Los Alamos.  

Today, you can visit the Los Alamos Downtown historic sites, but the sites on Laboratory land are not accessible to the public. However, the Department of Energy, Los Alamos National Laboratory, and the National Park Service collaborate to provide public tours of three sites on Laboratory property. Click here for more information on these tours and how to register for them.

Watch the video: Der Weg ins Atomzeitalter: Das Manhattan-Projekt Doku 2016